2018 ASHS Annual Conference

Illicium is an ancient genus and member of the earliest diverging angiosperms known as the ANA grade (Amborellales, Nymphaeales, and Austrobaileyales). These adaptable, broadleaf evergreen shrubs, including approximately 40 species distributed throughout Asia and North America, are valued for diverse culinary, medicinal, and ornamental applications. The study of cytogenetics of Illicium can clarify various discrepancies and further elucidate chromosome numbers, ploidy, and chromosome and genome size evolution in this basal angiosperm lineage and provide basic information to guide plant breeding and improvement programs. The objectives of this study were to use flow cytometry and traditional cytology to determine chromosome numbers, ploidy levels, and relative genome sizes of cultivated Illicium. Of the 29 taxa sampled, including approximately 11 species and one hybrid, 2C DNA contents ranged from 24.5 pg for I. lanceolatum to 27.9 pg for I. aff. majus. The genome sizes of Illicium species are considerably higher than other ANA grade lineages indicating that Illicium went through substantial genome expansion compared to sister lineages. The New World sect. Cymbostemon had a slightly lower mean 2C genome size of 25.1 pg compared to the Old World sect. Illicium at 25.9 pg, providing further support for recognizing these taxonomic sections. All taxa appeared to be diploid and 2n = 2x = 28 except for I. floridanum and I. mexicanum which were found to be 2n = 2x = 26, most likely resulting from dysploid reduction following divergence into North America. The base chromosome number of x = 14 for most Illicium species suggests that Illicium are ancient paleotetraploids that underwent a whole genome duplication derived from an ancestral base of x = 7. Information on cytogenetics, coupled with phylogenetic analyses, identifies some limitations, but also considerable potential for the development of plant breeding and improvement programs with this genus.